1. Field of the Invention:
This invention relates to apparatus for reproducing the informations from a tape-shaped recording medium which was run at two or more different speeds during recording. As such reproducing apparatus, there may be considered magnetic recording and reproducing apparatus, optical reproducing apparatus and many more various types of apparatus. The description will be, however, chiefly made of an example of the type of apparatus for reproducing video information from a magnetic tape on which television signals have been recorded, or a video tape recorder (hereinafter referred to as "VTR").
2. Description of the Prior Art:
Recently, high density magnetic recording has become possible, and VTRs capable of making long-time recording and reproducing have been developed and commercially manufactured.
These, for adaptation to the conventional format too, are made to operate with various selected time modes, for example, standard and long ones, during recording and reproduction in a single VTR item. In order to reproduce the picture recorded on the magnetic tape by such a dual time mode operating VTR, it is necessary that the same time mode be set up as was used in the recording operation. Otherwise, because the time mode would be different, a disturbed picture would be reproduced. Manual choosing of the required reproduction time mode while observing the reproduced images is very inconvenient to the user. On this account, according to the prior art, when recording, the tape is given one control signal (hereinafter referred to as "CTL" signal) for every one frame at the vicinity thereof. Then when reproducing, the number of revolutions of the capstan motor proportional to the distance the magnetic tape has run is sensed with a pulse generator, and how many pulses have been produced in the time interval of occurrence of the CTL signal is counted to examine whether or not the time mode is different between the recording and the reproduction. Upon detection of the difference, the preliminary setting of the time mode is automatically changed over.
Here such prior art is described by way of example with reference to FIG. 1. A magnetic tape 1 is moved in a direction indicated by arrow by a capstan 2 and a pinch roller 3.
The video signal, which has been recorded on tracks inclined to the length of the magnetic tape 1 by a rotating magnetic head (not shown) fixedly carried on a rotary drum as is well known in the art, is reproduced from the magnetic tape 1. The capstan 2 is driven by a motor 4 through an endless belt 5 to rotate at a prescribed speed. To sense the speed of rotation of the capstan motor 4, there is a frequency generator 6 of which output pulses therefrom proportional in number to the speed of movement of the magnetic tape 1 are applied via an amplifier 7 to a counter 8 at a clock input terminal CK thereof. A control head 9 picks up the CTL signals of repetitive at the frame rate, and its output is applied through an amplifier 10 and a waveform shaper 11 to the "reset" terminal R of the aforesaid counter 8. With such an input stage, the counter 8 recycles counting the number of pulses in a time interval from one to the next CTL signal and its outputs Q1 to Q4 are applied to a magnitude comparator 13 where they are compared with outputs of a reference control 12 in which a number is preset. When this reference number is exceeded, the output Q5 of comparator 13 takes a high level. That is to say, for the standard mode, the number of pulses counter 8 has counted in between the successive two CTL signals is assumed to be 44. Then if the recording has been operated in the long time mode, where the tape speed is halved, the CTL time interval becomes 1/2 times that of the standard mode. Therefore, when the magnetic tape which has been run at the long time mode during recording, is run at the standard mode during reproduction, the number of pulses counted in every one CTL interval is not 44 as is normal, but only a half of that, or 22. With the reference control 12 having preset therein an intermediate number between 22 and 44, therefore, when no more than the reference number is counted during reproduction at the standard mode, it is found that the recording has been performed in the long time mode. Conversely, when more than the reference number is counted, it is found that the recording was performed in the standard mode.
However, as some of the CTL signals may fail to be recorded, or as formats having nothing to record what is called the control signals from the first are employed, a problem arises that such automatic mode setting does not result.